The present invention relates to a cooling structure of a multi-cylinder engine, and particularly to a cooling structure of a multi-cylinder engine which includes a spacer inserted into a water jacket of a cylinder block of the engine.
Generally, vehicles with an engine are formed with water jackets for flowing coolant in the engine cylinder block and cylinder head. The coolant is introduced from the cylinder block at one end in a cylinder line-up direction into the water jacket of the cylinder block, and circulated inside the water jacket of the cylinder block and then into the water jacket of the cylinder head, so as to cool the part of the engine near combustion chambers.
Generally, the coolant circulated inside the water jackets of the cylinder block and the cylinder head is discharged to a radiator from the cylinder head at the other end in the cylinder line-up direction, cooled by the radiator, and then introduced into the water jacket of the cylinder block again from the one end of the cylinder block by a water pump.
In the case of cooling by the circulation of the introduced coolant to the water jackets of the cylinder block and the cylinder head as described above, an upper part of an inner wall of the water jacket of the cylinder block near the combustion chambers increases in temperature more than a lower part thereof. Therefore, the upper part is required to be cooled more than the lower part.
For example, JP2015-083790A discloses a structure in which a spacer having a vertical wall surface is inserted into a water jacket of a cylinder block to surround cylinder bores. Coolant is introduced from a coolant inlet formed in an outer wall of the water jacket of the cylinder block, and the coolant flow is rectified so that the coolant flows on an outer circumferential side of the vertical wall surface of the spacer, and also rectified to flow, in an upper part of the water jacket, toward an inner circumferential side of the vertical wall surface of the spacer through a plurality of openings formed in the vertical wall surface. Thus, an upper part of an inner wall of the water jacket of the cylinder block is cooled more than a lower part thereof.
The structure of JP2015-083790A is formed with the plurality of openings in portions of the upper part of the vertical wall surface of the spacer opposing to inter-cylinder-bore portions of the cylinder block, so that the coolant flowing to the inner circumferential side from the outer circumferential side of the vertical wall surface of the spacer flows to the inner circumferential side of the vertical wall surface of the spacer at the corresponding positions to the inter-cylinder-bore portions of the cylinder block and cools the inter-cylinder-bore portions.
With this structure, the coolant flowing on the outer circumferential side of the vertical wall surface of the spacer flows between an upper flange part and a lower flange part provided to the vertical wall surface. Additionally the coolant partially flows to the inner circumferential side of the vertical wall surface through the openings at the portions opposing to the inter-cylinder-bore portions of the cylinder block.
However, since the coolant partially flows toward the inner circumferential side of the vertical wall surface through the openings, the flow rate of the coolant flowing around the vertical wall surface decreases, and the amount of coolant flowing to the inner circumferential side through the opening disposed on the downstream side becomes smaller than that of the coolant flowing thereto through the opening on the upstream side. Thus, coolability of the coolant in upper sections of the cylinder bores may degrade.